Flowmeters and flow sensors are utilized in a number of applications, and have been adopted by the medical industry, chemical industry, automotive industry, and the food and beverage industry to name a few. It is often desirable to have an extremely low cost flowmeter solution, and in some environments a disposable flowmeter may be necessary. For example, in medical settings flowmeters may be contaminated with biohazardous material, which necessitates either autoclaving or disposal after use, both of which may prove costly.
Current technologies that may be considered low cost flow meters include peristaltic pump flowmeters, turbine meters, and differential pressure flowmeters. Even though these meters are considered low cost, they are still relatively expensive. Other than the tubing for the peristaltic pump, these meters would not generally be considered disposable.
It is well known that flow rates may be obtained from a peristaltic pump. The flow through a peristaltic pump may be calculated as a proportion of the rate of pump revolution. The flow rate may be calculated by simply multiplying the revolution rate by a calibration factor. Since tube diameters may not be consistent, elasticity of tubes may vary, and pressures both upstream and downstream of the pump may vary, calculated flow rates tend to be inaccurate. Additionally, by changing out tubes, recalibration may be necessary, which adds to the cost of operation.
Differential pressure flowmeters utilize a region of constriction in a conduit that creates a pressure drop across the constriction. As flow increases through the flowmeter, the pressure drop increases and is more easily measureable. Bernoulli's equation, as applied to such a flowmeter, states that the pressure drop across the constriction is proportional to the square of the rate of flow. By measuring the pressure before and after the constriction, the pressure drop may be measured and correlated with a flow rate. Differential pressure sensors, however typically exhibit low accuracy at low differential pressures/low flow rates. Additionally, accuracy may decline with wear and buildup. Furthermore, these flowmeters are not generally considered disposable due to their cost.
Turbine flowmeters are also well known in the art, and are used in a variety of applications. For example, a turbine is placed in a cylindrical bore of a flowmeter body, and fluid passes through the bore, which causes the turbine to rotate at a rate that is substantially proportional to the rate of fluid flow. However, at low flow rates, the relationship between turbine speed and flow tends to be nonlinear, so flowmeter accuracy suffers. For example, if a magnetic pick-up coil is used to detect rotation of the turbine, changes in the reluctance large enough to induce a detectable current change are largely absent at low speed. Therefore, a magnetic pick-up coil turbine flowmeter is a poor choice for low-flow systems.
In medical industries, for example, there is a need for a flowmeter that can be used in any number of medical devices, wherein bodily fluids are passed therethrough. Once the medical process is complete, the flow meter would need to be autoclaved or disposed of. Currently peristaltic pumps are the method of choice, but these devices are relatively expensive, not particularly reliable, and prone to inaccuracy, as noted above.
The embodiments described below provide an accurate, inexpensive, and disposable flow meter. It is an object to provide an embodiment for the measurement of fluid flow that is accurate, yet inexpensive. It is an object to provide an embodiment for the measurement of fluid flow that is disposable. It is an object to provide an embodiment for the measurement of fluid momentum utilizing diaphragm displacement. These and other objects are provided herein, and an advance in the art is achieved.